Drug delivery devices for setting and dispensing a single or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose as that of an ordinary syringe.
Drug delivery devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patient's suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable drug delivery devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous.
For instance, such devices comprise a housing to receive a cartridge being at least partially filled with the medicament to be dispensed. The device further comprises a drive mechanism, typically having a displaceable piston rod to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge can be displaced in a distal or dispensing direction and may therefore expel a pre-defined amount of the medicament via a piercing assembly which is to be releasably coupled with a distal or dispensing end of the housing of the drug delivery device.
Depending on the type of medicament and the way the medicament has to be prepared prior to be administered to a patient, particular drug delivery devices have to provide a medicament guiding structure, e.g. downstream of a cartridge but upstream of a dispensing end. Manufacturing of such fluid guiding structures or fluid guiding channels is somewhat crucial. Especially when the fluid guiding structure is made of plastic, in particular of thermoplastic material, a desirable miniaturization of fluid guiding structures or channel structures is difficult to achieve. For instance by way of injection molding processes complicated or multiply wound hollow channel structures cannot be realized.
Especially with drug delivery devices and applications it would be of particular benefit to provide fluid guiding channels with a comparatively small cross section in order to minimize a dead volume of the fluid guiding structure for not unnecessarily wasting precious or expensive medicaments or the like substances to be guided therethrough.
Moreover, fluid guiding plastic components should be substantially inert or highly compatible to the medicament or substance to be guided therewith. Hence, the range of plastic components suitable for medicament guiding purposes is rather limited.
In general, small sized channel structures can be manufactured by providing a member featuring a channel-forming groove or recess extending across a surface portion. By covering the surface portion with a cover part and by bonding cover part and said member together, a closed fluid-guiding channel structure can be provided in principle. Bonding of the member and the cover part may be provided by way of laser welding or ultrasonic welding as well as by making use of adhesives. Such mutual bonding of member and cover part involves application of heat, which may eventually deteriorate the chemically inert properties of the respective plastic material.
Moreover, chemically inert plastic materials are rather unsuitable for e.g. laser welding due to insufficient light absorption properties. Enhancement of light absorption can in principle be attained by embedding light absorbing particles, such like soot particles, in the bulk of such plastic materials. However, this may further deteriorate the purity of the plastic material and pre-defined as well as required chemically inert properties may no longer be met.
Also, when bonding the member and the cover part together by means of an adhesive, a portion of the adhesive may intrude into the channel structure, thereby enhancing a risk, that the medicament flowing therethrough gets contaminated.